In an embroidery lace machine having mechanisms such as needles, shuttles, thread carriers, borers, borer depth controllers and the like, it is known to control the convention of each mechanism relative to the main driving shaft by means of electrical control signals.
Each of the mechanisms to be driven is to be connected to or disconnected from the main driving shaft at a time when the rotating driving shaft reaches a predetermined angular position. This predetermined angular position or timing varies for each mechanism. It is known to obtain the required timing signals for controlling the connection and disconnection of the controlled mechanisms of the machine in two ways.
As shown in FIG. 10 of the accompanying drawings, one known way of generating the required timing signals is to provide a main driving shaft 1 of the machine with a plurality of cam dogs 2 for actuating respective detector switches 3. The cam dogs are provided in pairs with the two cam dogs of each pair respectively defining the points of connection and disconnection of a corresponding mechanism. For example, in FIG. 10, one cam dog 2A of the pair of cam dogs 2A, 2B, actuates a detector 3A associated with the connection of a needle to the driving shaft and the other cam dogs 2B actuates a detector 3B associated with the disconnection of the needle from the driving shaft. Similarly, the pair of cam dogs 2C and 2D are associated with respective detectors 3C and 3D respectively associated with the connection of a shuttle to the driving shaft and the disconnection of the shuttle from the driving shaft. The arrow 4 indicates that the main driving shaft 1 is connected to the needle, shuttle and any other controlled mechanisms driven from the driving shaft by suitable drive connections.
Another known way of generating timing signals for the connection and disconnection of the controlled mechanisms is to couple the main driving shaft with cylindrical signal generating rings having electrically conductive portions and electrically non-conductive portions constituting respective timing signal generators corresponding to the mechanisms to be controlled so that timing signals may be generated according to interruptions in electrical current picked up from the rings.
However, the prior art constructions have a drawback in that troublesome mechanical modifications, such as changing the angular positions of the cam dogs or of the rings are necessary in order to adjust or change the timing of the operation of the mechanisms driven by the driving shaft. Moreover, the accuracy with which angular positions detected in the known constructions is not good. Furthermore, the prior art constructions require as many detecting means as there are mechanisms to be driven from the driving shaft, and accordingly the system becomes complicated, giving rise to the possibility of malfunctioning.